Clash-of-clans – Link an iOS 5 and an iOS 8 device in Clash of Clans

At first, you must log out from your existing game center account "Before" you wipe all of your data. After you do that, you install the game and after you install it, play it. After you do all of that, you will be noticed to sign in to your game center id. You just use your game center id without having a new GC id. After you sign in, you will be noticed again with another pop up saying do you want to reload your village at town hall level "X"? If you want to totally reset your village, just tap the no button. And if you want to reload it, just tap yes :) simple, right? And 1 more thing... don't use backed up data if you are still in the "New user" page, you must get it back "AFTER" your device already passes through the new setting ("New user" page) of your new device. (Back it up after you install clash of clans)

If you have already used your one sync, then you are kind of stuck. When switching devices, they allow you only one sync. This is for security reasons, but it kind of acts as an inconvenience here. There is almost no way to get your account synced after that. I would recommend contacting Supercell if you are desperate.